Antenna systems are widely used in both ground based applications (e.g., cellular antennas) and airborne applications (e.g., airplane or satellite antennas). For example, so-called “smart” antenna systems, such as adaptive or phased array antennas, combine the outputs of multiple antenna elements with signal processing capabilities to transmit and/or receive communications signals (e.g., microwave signals, RF signals, etc.). As a result, such antenna systems can vary the transmission or reception pattern (i.e., “beam shaping” or “spoiling”) or direction (i.e., “beam steering”) of the communications signals in response to the signal environment to improve performance characteristics.
A typical phased array antenna may include, for example, one or more element controllers connected to a central controller. Among other functions, the element controllers process beam control commands generated by the central controller (e.g., beam steering signals and/or beam spoiling signals) and provide output control signals for each of the phased array antenna elements. More particularly, each antenna element may have a phase shifter, attenuator, delay generator, etc., and the output control signals from the element controller may be used to control a phase, attenuation, or delay thereof. Thus, the transmission or reception pattern may be varied, as noted above. In such phased array antennas, temperature changes may have a significant impact on phase shifters, attenuators, or operating frequencies of the phased array antenna that may result in undesirable signal characteristics. This problem is compounded by the fact that the power amplifiers driving these phased array antennas generate a relatively considerable amount of heat. Therefore, maintaining the operating temperature within a desirable range is critical to the performance of a phased array antenna system.
Phased array antennas are typically designed using either a “brick” architecture or a “tile” architecture. In a brick architecture, the active and passive communication components are mounted on rectangular Transmit Receive Modules (TRMs) that resemble bricks, and are placed behind the radiating elements perpendicular to the array face. In a tile architecture, the components are placed on small modules that mount parallel to the array face, much like common tiles. FIG. 1 depicts a schematic side view of a portion of a phased array system utilizing a tile architecture, including a transceiver device in the form of an integrated circuit (IC) chip 10 (such as a Monolithic Microwave IC or MMIC) mounted on an insulating substrate 20. The insulating substrate is separated from an antenna substrate 30 by a ground plane 40. Mounted upon the antenna substrate is an antenna element 50 for transmitting and receiving radio signals. The ground plane 40 is formed of an electrically conductive material and includes an opening 42 overlying the antenna element 50. The insulating substrate 20 is typically formed of ceramic material, which is an excellent electrical insulator and also a poor heat conductor. Therefore, a cooling manifold 60 is usually located behind the chip 10, on the side opposite the antenna elements 50. This approach to cooling phased array antenna systems has been moderately successful, but entails the additional costs and complexity associated with the cooling manifold fabrication and attachment.
Components on tiles are typically mounting using standard “pick and place” and wirebonding techniques, which are costly and time consuming procedures that prohibit cost effective manufacturing of very large arrays. Coupling between the input/output antennas and the MMIC circuit is typically accomplished by transitioning off the communication chip using a standard technique (e.g. wire bonding), then transitioning to the antenna using other types of transitions. This technique has been known to adversely impact the efficiency of energy transfer between the communication chips and the antennas due to inaccurately placed or lossy wirebonds.
To avoid problems associated with the creation of plated-through holes (or vias), aperture coupling is a commonly used method for exciting patch antennas and has a number of advantages over other methods such as probe coupling or in-plane excitation from components mounted next to the antennas. Probe coupling through a ground plane aperture requires additional processing steps to provide conductive feed-through holes (vias) in the antenna substrate, which restricts the types of materials used for the antenna substrate (e.g., Sapphire is difficult to drill or etch through). On the other hand, mounting the MMIC components on the antenna substrate next to the antenna elements may eliminate the need for plated through holes, but this approach places the MMIC components directly within the radiated fields of the antenna array, potentially causing spurious coupling between different sections of the transmit or receive circuitry, and possibly causing spurious scattering of the radiated fields due to the additional circuitry present on the antenna layer. Additionally, this also reduces the surface area available for chip placement, which is already severely limited by the large areas typically occupied by the antenna elements. Aperture coupled patch antennas eliminate these issues by shielding the MMIC components safely behind a ground plane, and utilizing ground plane apertures to efficiently couple the signals to and from the antenna elements, without the need for plated through holes. As further shown in FIG. 1, aperture coupling entails transitioning off the chip 10 using a wire bond 70 to a conductive microstrip 80 which couples electromagnetically with the antenna element 50 through the opening 42 in the ground plane 40.
The present invention further improves upon the design of phased array antennas and enhances their operating efficiency by more efficient coupling and improved cooling performance.